Process for manufacturing reinforced composites

ABSTRACT

This invention relates to a process for manufacturing composites and laminates reinforced with continuous or long fibers and/or filaments. The process includes the subsequent steps of (a) forming a preform of reinforcing material by arranging a green tape, ribbon, sheet or cloth including a number of continuous longitudinally oriented fibers or filaments which are spaced from each other by uniformly distributed particles, bonded by a flexible binder, (b) removing or converting a major portion of the binder into matrix material and, if applicable, (c) filling the voids and cavities with matrix material. Further, this invention relates to a process for manufacturing composites and laminates reinforced with chopped-aligned fibers and/or filaments, which includes chopping a green tape or ribbon as defined above, mixing the chopped tape or ribbon with a binder, lubricant and/or matrix material and forming mouldings from this mixture by any moulding method.

BACKGROUND OF THE INVENTION

The invention relates to reinforced shaped composites and laminates.More specifically, the invention relates to a process for manufacturingshaped composites and laminates reinforced with long or continuousfibers and/or filaments or chopped-aligned fibers or filaments, such ascarbon matrix composites (FRCC's), ceramic matrix composites (FRCMC's),glass matrix composites (FRGMC's), glass-ceramic matrix composites(FRGCMC's), metal matrix composites (FRMMC's), intermetallic matrixcomposites (FRIMC's), cement, concrete or gypsum matrix composites andreinforced plastic composites and to filament tapes, ribbons, sheets orcloths for use in said process.

Composites and laminates, i.e. combinations of two or more materials,comprising matrix material(s) and reinforcing fillers, which form abonded quasi-homogeneous structure with synergistic mechanical andphysical properties compared to the basic matrix and filler materials,form an important class of construction materials in modern technology.Composites may be of two different types, viz. composites comprising amatrix with discontinuous filler system particles, platelets, whiskers,i.e. short fibers, flakes and chopped fibers, i.e. fibers of a lengthbetween say 3 mm and about 20 cm and composites comprising a matrix withpreform moulding of long or continuous fibers and/or filaments.Laminates generally comprise a matrix with a number of laid up webs oflong or continuous fibers and/or filaments or chopped fibers orfilaments.

In principle the composites with chopped and in particular withcontinuous fibers and/or filaments and the laminates form preferableconstruction materials because they combine desirable intrinsic physicaland/or chemical properties of the matrix with favourable strength andstiffness properties derived from the fibers and/or filaments. Thechopped fibers or filaments and the long continuous fibers or filamentsare basically used in four configurations (vide Kirk Othmer,Encyclopedia of Chemical Technology, third Edition, Supplement Volume,page 261) of which the unidirectional configuration (long or continuousfibers or filaments arranged substantially parallel to each other) andchopped-aligned configuration (chopped fibers or filaments all arrangedin the same direction) in principal give the best performance. Becausefibers afford significant control over the internal structure of thecomposite and because of their high aspect ratios (ratio of length todiameter), long, continuous fibers are the reinforcing elements ofchoice in high performance composites.

However, according to Mittnick and Mc. Elman in a paper entitled"Continuous Silicon Carbide Reinforced Metal Matrix Composites"presented at the SME Metal Matrix Composites '88 Conference, September1988, pages 91-99, it is difficult when manufacturing composites whichgenerally involve complex geometric shapes, to position continuousfibers during the fabrication process. The system described by Mittnickand Mc. Elman, the so called "green tape" system, the "plasma-sprayedaluminium tape" system and the "woven fabric" system of which the latteris said to be perhaps the most interesting, are indeed only suitable formanufacturing laminates of rather simple shape. In all these systemsseparate fiber sheets, each comprising a single layer of straight andparallel fibers held together by a temporary or permanent binder orcross-wave, are sequentially laid up into a mould in the requiredorientation to fabricate laminates. The method described for making thegreen tape comprises winding the fibers or filaments onto a foil-coveredrotating drum, overspraying the fibers with a (temporary) resin binder,followed by cutting the layer from the drum to provide a flat sheetwhich is used for making a preform moulding by laying up. This methodrequires a careful control of the winding operation to keep the fibersor filaments parallel with the correct spacing. But even then, when thesheet or laid up and subsequently the temporary resin binder is removed,the orientation of the filaments gets at least partly lost.

In European patent application EP 249927 it is suggested to applybundles of continuous fibers or filaments having fine particles, shortfibers and/or whiskers deposited on the individual surfaces of thecontinuous fibers of filaments as reinforcing system for compositesand/or laminates. These bundles of continuous fibers or filaments withfine particles, short fibers and/or whiskers deposited on the individualsurfaces of the continuous fibers or filaments are formed by introducingsaid particles, short fibers and/or whiskers into a bundle of loosefibers or filaments. Under these circumstances a more or less uniformand homogeneous result is only obtained when both fine particles andshort fibers or whiskers have been deposited on the individual surfacesof the continuous fibers or filaments. When only fine particles havebeen deposited on the surfaces of the continuous fibers, the fibers tendto bunch and when only whiskers or short fibers have been deposited onthe surfaces of the continuous fibers or filaments, it is difficult toprevent the fibers or filaments from contacting each other. Filamentsare easily damaged by the (sharp) materials deposited on the surfaces ofthe other filaments, and deposited material easily falls out andpotentially damages shaping equipment.

A general problem encountered by applying usual preforms, produced fromfiber products, is that the matrix cannot infiltrate sufficiently andhomogeneously in between the bundles and the monofilaments of thereinforcement fibers. The interstitial space within the fiber bundles isoften much smaller than the spaces between the fiber bundles used toproduce the preform, and the rate of bundles infiltration relative tothe preform infiltration become insufficient.

An object of the invention now is to provide composites and laminatesreinforced with long or continuous fibers and/or filaments in aunidirectional configuration or with long chopped fibers or filaments ina chopped-aligned configuration. More in particular an object of theinvention is to provide a process for manufacturing such composites orlaminates in a cheap, easy and reliable manner, without the problemsmentioned herein before. A further object is, to enable the applicationof automated and/or controlled thermoplastic typefabrication/melt-shaping techniques to shape complex preforms. A furtherobject is, to avoid damage and/or degradation to thefibers/monofilaments during shaping and/or processing. A further objectis, to avoid clustered fibers in the shaped preform. A further object isto substantially avoid preform shrinkage. A further object is to"tailor" the permeability of the preform. A further object is to easethe forming of a tailored matrix mix. A further object is to reduce thenumber of production steps, and/or production time and/or firing cycles.A further object is to obtain net-shape or near net-shape compositearticles and/or integrated systems substantially eliminating costlymachining. A further object is, to provide a novel green tape, ribbon,sheet or cloth with long or continuous fibers and/or filaments, which issuitable for use in the process of manufacturing composites or laminatesaccording to the invention and which can produce a dense compositematerial. Further objects and advantages of the invention will appearfrom the following description of the principles and preferredembodiment of the invention.

It has been found that a correct, stable orientation of long orcontinuous reinforcing fibers or filaments is easily obtained when anumber of long or continuous reinforcing fibers or filaments, say tow,roving or yarn, of such fibers or filaments is spread out in a singlelayer or a limited number of multi-layers, fibers or filaments arespaced by particles, such as granules, platelets, whiskers or flakeswhich are uniformly distributed between the fibers or filaments and thisarrangement is fixed by means of flexible, organic- or other binder,thus forming a green tape, ribbon, sheet or cloth and that such a tape,ribbon, sheet or cloth can be arranged (e.g. by braiding, compressing,laminating, pultrusion, rolling, winding or weaving) to form a preformmoulding wherein the fiber/monofilaments are protected duringhandling/shaping and the orientation and spacing of the fibers orfilaments are maintained, thanks to the binders. These preform mouldingsthen are used as a reinforcing structure in manufacturing advancedcomposites and laminates, in particular carbon, ceramic, glass,glass-ceramic, metal and intermetallic composites. The invention isbased on these findings.

SUMMARY OF THE INVENTION

In one aspect this invention relates to an improved process formanufacturing composites and laminates reinforced with continuous orlong fibers and/or filaments, such as carbon matrix composites (FRCC's),ceramic matrix composites (FRCMC's), glass matrix composites (FRGMC's),glass-ceramic matrix composites (FRGCMC's), metal matrix composites(FRMMC's), intermetallic matrix composites (FRIMC's), cement, concreteor gypsum matrix composites and reinforced polymers, which includes thesubsequent steps of (a) forming a preform of reinforcing material byarranging (e.g. braiding, compressing, laminating, laying up, windingand/or weaving) a green tape, ribbon, sheet or cloth comprising a numberof continuous longitudinally oriented fibers or filaments which arespaced from each other by means of uniformly distributed particles,bonded by means of a flexible binder, (b) removing or converting a majorportion of the binder into matrix material and, if applicable, (c)partly or completely filling the voids and cavities with matrixmaterial.

In another aspect the present invention relates to an improved processfor manufacturing composites and laminates reinforced withchopped-aligned fibers and/or filaments, which includes chopping a greentape or ribbon comprising a number of continuous longitudinally orientedfibers or filaments which are spaced from each other by means ofuniformly distributed particles, bonded by means of a flexible binder,optionally mixing the chopped tape or ribbon with a binder, lubricantand/or matrix material and forming mouldings from this mixture bycentrifugal, compression, injection, reaction, extrusion, cast, vacuumor other moulding. Preferably this process also includes the step ofremoving or converting a major portion of the binder into matrixmaterial after the moulding step.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

It is an essential feature of the invention that the green tape, ribbon,sheet or cloth comprising a number of continuous longitudinally orientedfibers or filaments which are spaced from each other by means of a dosedamount of uniformly distributed particle material(s) oftailored/predetermined size, bonded by means of a flexible binder, areused as a starting material for manufacturing the preform moulding orfor producing an injection moulding mixture comprising chopped ribbon ortape and possibly additional binder, lubricant and/or matrix material.Such tapes or ribbons preferably contain a tailored content of matrixparticles mixed with a tailored content of flexible binder so that theyeasily can be arranged in the desired shaped preform moulding, whilemaintaining the orientation and spacing of the filaments and thedistribution of the spacer particles.

These tapes or ribbons can suitably be manufactured by using standardtechniques, such as adapting the teaching of UK patent 1259085. Inagreement with the teaching of this patent, filaments grouped togetherin the form of a filament bundle or low twist thread, a roving or tow,are separated, e.g. by passing them through a venturi tube through whicha fluid flows at high velocity or by giving all the filaments anelectrostatic charge of the same sign so that the filaments repel eachother, followed by applying a powdery treating agent comprising spacerparticles and particles of a flexible low melting binder on the spreadfilaments and subsequently melting the binder to fix the spacedfilaments and spacer particles.

A preferred prior art method for manufacturing the tapes or ribbons isthe method disclosed in European Patent 274464, which is cited here byway of reference. In accordance with this patent, but using the specificcomponents of the present invention, bundles of filaments, such asrovings, are spread out in a single layer wherein the individualfilaments are close together and a suspension of spacer particles andparticles of a flexible, low melting binder in a fluid stream(preferably a gas stream) is subsequently directed onto the spacedbundle under a controllable pressure such that the filaments in thespaced bundle are separated by the fluid stream and the particlespenetrate uniformly between the filaments, and finally melting thebinder to fix and encapsulate the filaments and spacer particles.Especially by the latter method a very uniform distribution of thespacer particles is obtained in a continuous process.

The type of reinforcing fibers or filaments used must be adapted to thetype of reinforced composite or laminate made. Preferably, for any typeof reinforced composite or laminate monofilaments are used, which giveoptimum strength with a minimum of handling problems.

Such filaments may have diameters between about 0.3 μm and 0.3 mm andpreferably have diameters between 1 μm and 0.2 mm and in particularbetween 2 μm and 0.15 mm.

Further, for any type of reinforced composite or laminate thereinforcing filaments or fibers should readily and optimally bond to thematrix used. For reinforced plastics the fibers or filaments in thegreen tape or ribbon preferably are high strength, high stiffness, lowdensity fibers; this gives the most favourable combination ofproperties. Suitable fibers or filaments for this use are chosen fromthe group of aramid, boron, carbon, ceramic, glass, graphite, metal,silicate or other fibers.

For refractory reinforced composites or laminates, which generallyrequire treatment at high temperatures and/or pressures to fill thevoids or cavities in the preform mould, the reinforcing filaments orfibers must resist degradation in contact with molten, reaction bondedor sintered matrix materials. For this purpose the fibers or filamentsin the green tape, ribbon, sheet or cloth preferably are refractory highperformance fibers or filaments or fiber hybrids suitable for use inFRCC, FRCMC, FRGMC, FRGCMC, FRMMC, FRIMC and other composites andlaminates. Preferably those fibers or filaments are chosen from thegroup comprising carbon or graphite, possibly protection coated, typesbased on pitch or polyacrylonitride (PAN) precursor, or oxides,carbides, nitrides and borides of elements from group IIIA and IV A ofthe Periodic System and mixed oxides, carbides and nitrides of elementsfrom group III a, IV a, III B through VII B and VIII of the PeriodicSystem. Particularly suitable are coated carbon or graphite, alumina,alumina-boriasilica, aluminum nitride, alumina-silica, boron, boroncarbide, boron nitride, boron nitride, magnesia, mullite, nitride,single-crystal sapphire, high purity silica, silica, siliconcarbonnitride, silicon carbide, silicon nitride titanium diboride, andzirconia fibers or filaments. Metallic types such as e.g. beryllium,stainless steel, molybdenum, titanium, and tungsten may also be used asfiber material. Synthetic diamond fibers can also be used.

The chosen reinforcing fibers or filaments are processed as describedabove, e.g. according to the teaching of UK patent 1259085, butpreferably according to the teaching of EP 274464 to impregnate themwith a mixture of spacer particles and binder particles. The function ofthe spacer particles is to separate the fibers or filaments uniformlyover a certain distance and maintain the general longitudinalorientation of the fibers or filaments. To reach this effect, the spacerparticles preferably are flakes, granules, platelets and/or whiskers andeither consist of an inert material which may be an additionalreinforcing component, or consist of a material which may form acomponent of the matrix. The characteristic dimensions of these flakes,granules, platelets or whiskers should be such that the reinforcingfibers or filaments are correctly spaced. In practice this means thatthe spacer granules and the flakes, platelets or whiskers have anaverage diameter and thickness, respectively, of the same order orpreferably smaller than the thickness of the fibers or filaments.

The term "binder" as used herein and in the claims is meant to definethe constituent or compound which holds the other components together;the agent applied to bond the fibers and particles prior to laminatingor molding. The function of the binder is finally to bond, encapsulateand protect the fibers or filaments which are spaced from each other bymeans of the uniformly distributed spacer particles, as well as thosespacer particles to a stable, shapeable, flexible tape, ribbon, sheet orcloth. For this purpose a flexible binder is used, which may be apermanent binder, e.g. a matrix plastic material when manufacturingreinforced plastics (e.g. rigid, highly crosslinked polymer having highthermal stability), or may be a temporary binder which must be removedor converted before introducing the second phase matrix material.

In the process of this invention for manufacturing composites andlaminates reinforced with continuous or long fibers and/or filaments, atemporary binder is used, a major portion of which is removed orconverted into matrix material in step (b).

Suitable temporary binders are natural or synthetic polymers andsynthetic waxes having a low melting point, or mixtures thereof, whichin step (b) are removed by heating. As waxes preferably petroleum waxesare used, because they are cheap and have good binding properties.Especially microcrystalline waxes which are ductile to tough arepreferred. As polymer a material which leaves none or minimum residuesafter removal from a preform, especially a clean burning polymer such asa polymethyl-metacrylate, polyalkene carbonate, polypropylene carbonateor a olefine polymer, preferably polyethylene or polypropylene, or awater soluble binder material, e.g. methylcellulose, are preferred. Theyare cheap, have reasonably low melting points of the order of 150° to185° C. and have a good binding power, leading to preferable flexibletapes, ribbons, sheets or cloths.

Preferably binders are recycled in the feedstock. Debinding time (ortime required for binder removal) is reduced, since the matrix paticlespresent between the monofilaments keep the filaments spaced, and thepreform or molded structrue becomes more and more porous duringdebinding.

Examples of temporary binders which may be converted in step (b) includethe following:

In the specific case wherein carbon material forms all or part of thematrix material, e.g. carbon/carbon composites, a pre-carbon polymerbinder/precursor is used which leaves an appreciable mass and volume ofcarbon after pyrolysis, e.g. a bulk mesophase/pitch, epoxy, furan,furfuryl alcohol, furfuryl ester, polyarylacetylene (PAA), polyamide(PA) polybenzimidazole (PBI), polyphenylenesulfide (PPS) or phenolicresin or mixture hereof.

In the specific case wherein ceramic material forms all or part of thematrix material, e.g. SiC or SiN composite, the binder, or part of it,is a precursor material with high ceramic char yields, which in step (b)is converted into ceramic material by heating/chemical synthesis. Such abinder is preferably a silicon based organo-metallic compound, apolysilane or polysilazane. Pyrolysis of polymeric metallo-organic mixesis a cost-effective and lower temperature route to produce ceramicmaterials while polysilazanes are being used to produce SiN ceramicmaterials. Many new precursor materials are presently being developed.

The binder is generally used in the form of powder. The particle size ofthe binder is dependent upon the impregnation process used, it may besmaller, equal or larger than the particle size of the spacer granules,whiskers of flakes, e.g. between about 0.1 μm and 50 μm or more, toresult in a uniform distribution of the binder particles between thefibers or filaments and the spacer elements after final distribution ofthe binder, preferably by melting. Liquid precursor which becomes solidat environmental temperature can also be used as a binder.

The fibers or filaments, the spacer particles and the binder are used insuch proportions that indeed a uniform and stable tape, ribbon, sheet orcloth is obtained which is sufficiently flexible to be arranged intopreform which gives the desired reinforcement to the composites orlaminates which are finally made by introducing matrix material andconsolidation/ densification of the shaped article. If desired, thebinder polymers may contain a plasticizer to improve the flexibility.Polymer and wax mixtures may be used. This result is reached with aproportion of fibers or filaments of about 5 to 7 vol. % calculated onthe volume of the tape, ribbon, sheet or cloth and preferably 20-55 vol.% and more preferably 30-50 vol. % and with a proportion of spacerparticles of about 3-50 vol. % and preferably 5-30 vol. % andmore-preferably 10-25 vol. % calculated on the volume of the tape,ribbon, sheet or cloth, the remainder being binder.

Besides the fibers or filaments, the spacer particles and the binder, ifdesired for reasons of process or results, also small amounts of furtheradditives, such as additions, chemical activators, colorants, dopants,foams, hollow fillers, lubricants, nucleating agents and/or reactantscan be added f.e. to improve the surface properties of the fibers orfilaments and possibly of the spacer particles, and to obtain a gooddistribution of the filler.

Particles of a reactive material are possibly encapsulated by a thinlayer of non reactive material, preferably by a (precursor) binder,prior to handling/impregnation/infiltration. This substantiallyeliminates explosion and oxidation danger and eases the precautionsrequired to handle fine reactive metal particulates e.g. by inert gasblanketing.

The flexible green tape, ribbon, sheet or cloth, which is made in thisway retains the orientation and the spacing of the mono-filaments andthe distribution of the particles, and can be fabricated/melt-shapedlike a flexible thermoplastic prepreg into a carefully engineeredpreform by braiding, compressing, laminating, pultrusion, rolling,stacking, weaving and/or winding, or can be chopped, optionally followedby mixing the chopped tape or ribbon with binder and/or lubricant and/oradditional particle material, suitable for moulding and formingmouldings by any usual molding method. The term "preform" as used hereinand in the claims is meant to define the preshaped fibrous reinforcementformed to a desired shape prior to being placed in a mold.

In order to ease the forming of the preform, it generally is ofadvantage to supply a monitored heat source in order to soften thebinder, thus improving shaping-flexibility of the "green yarn". In thisway complex shapes (such as 3-D, Adjacent Yarn Position Exchange(AYPEX), a special type of three-dimensional braiding, knitting,multi-layer weaving and hybrid weaves which are combinations of 3-Dorthogonal weaves and 3-D braids) with selective yarn reinforcement caneasily be preformed. The homogeneity of the preform determines theuniformity of the final articles and products. Heat and pressure can beapplied to improve this homogeneity. The original separation between themono-filaments and/or the mono-filaments distribution which is presentin the "green yarn" is substantially maintained during shaping of thepreform. Fiber-to-fiber contact is highly eliminated, which preventsmonofilament breakage or damage and also improves transverse strengths.

For refractory reinforced composites or laminates, the fibrousparticulates/powdery shaped (green) preform is then transferred to amould and:

the precursor polymer binder is processed (chemical synthesis/pyrolysisof polymer precursor), or

the "clean-burning" binder is removed, by any conventional removalmethod.

During the above-mentioned treatment, cavities/void spaces can developin between the fibers or filaments and the spacer particles, being holdin place in between of the mono-filaments.

After processing the product is a porous preform with homogenouslydistributed fine pores in between of the monofilaments and the spacerparticles. The size of the pores is controlled by the size and quantityof the spacer particles and the volume of the precursor and/orclean-burning binder used to impregnate the fibers/monofilaments.

The original shape is substantially maintained because the uniformlydistributed matrix particles hold the fibers/monofilaments spacedbefore, during and after chemical synthesis/pyrolysis of polymerprecursor and/or binder removal. Preform shrinkage is substantiallyavoided. Due to the presence of these particles, homogeneouslydistributed in between of the monofilaments, the mono-filaments are holdin positive "angle plied" alignment and remain well spaced side by sideacross the preform, which gives an improved flexural strength of thepreform. The permeability of the preform is highly governed by thehomogeneous distribution of the particles/mono-filaments, and canaccurately be engineered/optimized by choosing the dimensions of theparticles which are entrapped in between of the fibers/monofilamentsduring the impregnation process, and which keep the mono-filamentsproperly spaced during following pyrolysis of the polymer precursor orremoval of the binder, and subsequent preform reinfiltration/CVI.

After the permeable preform has been obtained in this way, the voidspaces between the mono-filaments and the particles are then filledup/reinfiltrated by any of the usual preform reinfiltration methods orcombinations thereof, e.g. by gravity, continuous, inert gas pressure orvacuum infiltration with a matrix material (in liquid/melt or slurryform) by chemical vapour infiltration (CVI), by chemical/diffusion orreaction bonding, or by forming a matrix material in situ by reaction atrelative low temperatures between infiltrated liquid or solid/slurrymaterials and appropriate gases (e.g. directed metal oxidation).Infiltration lengths can be increased with no or lower pressure and inshort times and preferably at lower temperatures, and a more completeand faster infiltration of the second phase matrix material is obtained,thus reducing the danger of fiber degradation. In these filling stepsadditives can be included to improve the flowability of infiltrationmaterial(s) in the case of a liquid or slurry and in the case of ceramicmatrix material a sintering aid can be added in order to avoidinterface-strengthening. If required this infiltration can be repeated,probably after a heat and/or pressure treatment, until the pores areminimized. The homogeneity of the preform intra monofilament spacing andthe more complete infiltration step of the preform leads to asubstantially minimization and uniformity of shrinkage. Because of thesignificant amount of matrix material already present, reinfiltration tofull density can be done at lower pressures and in a considerablyshorter time than with the usual infiltration/CVI process, and processcost-efficiency is enhanced. The void spaces between the mono-filamentsand the particles may alternatively be partially filled with a matrixmaterial by any of the above-mentioned methods. The voids are onlyfilled to a predetermined extent, which allows the manufacture ofarticles such as membranes, filters, catalyst supports and bio-compositematerials still possessing pores.

The process of the invention is ideal for structural compositessubmitted to high stresses. The shaped composites or laminates obtainedby the process of the invention are suitable for high performanceapplications, such as in aerospace, automobile, chemical andpetrochemical, fusion or plasma reactors, grinding tools, defence andother, where continuous and long fiber reinforced composites, likecarbon, carbon/ceramic, ceramic, glass, glass/ceramic, metal,intermetallic and others are and will be required. Especially aerospaceapplications need stiff very high performance materials, e.g. forair-breathing propulsion systems, such as gas turbine components,heat-shields, rocket nozzles, ramjet combustors and both primarystructures and airframes for reusable aerospace (hypersonic) vehiclesand satellites, that can be fabricated into complex shapes. Specialfeatures can be built in e.g. electrical conductivity/discontinuity/heating, magnetic, shape memory, thermal conductivity.

Functionally Gradient Materials (FGM), wherein a certain material orcombination of materials gradually changes its composition along thethickness or shape, and becomes a different material or combination, iscrucial for the production of engine parts and airframe and propulsionsystems of future high speed airplanes/space planes. In theseapplications lightweight construction materials are demanded. Thesematerials must be able to withstand higher temperature than conventionalmetals and still demonstrate high strength and impact resistance, e.g.super heat-resistant structural materials wherein ceramic material onone side provides the heat-resistant function and metal on the otherside provides the strength property and the composition in one articleor shape gradually varies from one side to the other. Other examples areCarbon-Carbon/Ceramic gradients etc. Since there is no interface betweenthe two materials, problems with boundary by thermal stress at theboundaries is avoided.

Other combinations can be engineered based on abrasion, chemicalresistance, density, flaw, friction, hardness, melting point, stiffness,strength, thermal expansions, toughness, wear resistance, etc. andcombinations thereof.

Chemistry/Compositions/Microstructure of gradient materials can beengineered, e.g. by applying precursors, CVD, PVD or other methods orcombinations thereof of infiltration/impregnation, e.g. precursors, bothhigh yields polymer for liquid infiltration and gasses for CVI.

The application of pressure and/or temperature gradients during theinfiltration/impregnation can improve processing results. Membranes,filters and catalyst supports for environment and other applications areproduced, as a result of the potential to tailor the predeterminedporosity, whereby charged molecules and/or active chemical groupings canbe added to membrane surfaces or infiltrated, in the pores, possibly ina gradual manner.

Superconductor composites in the form of coils, tubes, wires or othershapes can be produced by extrusion or other methods of shaping, e.g. byusing superconductive oxide particles and/or fibers possibly mixed withorganometallic precursors of superconductive oxide.

Applying electricity, microwaves, radiation or other energy source to ashaped composite can, dependent upon the constituents, modify certaincharacteristics of the composite, e.g. bonding, chemical resistance,electrical conductivity, electro optic, magnetic, porosity and others,as well as combinations thereof.

Bio-composite materials that mimic biological organisms can be made,e.g. artificial bones where part of the porosity can be infiltrated withmedical "donors/precursors" and porosity can assist natural bonebonding/forming. On the other hand electro-ceramic, shape memory alloys,piezoelectric and magnetostrictive materials are increasingly beingapplied.

In order to obtain "smart materials and structures" based on carbon,ceramic, glass, metals and the like, it is possible to include all sortsof insertions in the pre-shape in order to monitor structural integrityduring moulding, acoustic-, vibration control and other active control,damage- and failure detection and thermal expansion during use of theformed materials and structures. Insertions could be: e.g. actuators,piezoelectrics, shape Memory alloys and fibers, strain sensorsespecially fiber-optic strain rosettes.

EXAMPLE 1 Continuous Graphite Fiber Reinforced--Aluminum-Magnesium-SiCParticulate Structural Aircraft Parts

Continuous protection coated graphite monofilament yarn (diameter 10 μm)is homogeneously impregnated with a mixture of powderyAluminum/Magnesium alloy (Al-Mg) of particle size 8 μm, SiC particles (1μm), and powdery polypropylene binder material (particle size 15-20 μm).The preform has a pre-defined selective monofilament reinforcementaccording to the processing requirements and the characteristicsdictated by the end-use requirements of the article. The alloyedmatrix/binder mix content is tailored, taking into account theflexibility required for subsequent complex shaping. Homogeneousimpregnation is performed at high speed and under inert gas, using thecontinuous binder/particulate/powder impregnation process as describedin EP 274464. The composition of the tape is 50 vol. % graphitemonofilaments, Al-Mg alloy powder matrix spacer particles 20 vol. %including SiC particles and binder 30 vol. %. (The Mg content being 6weight % of the Al-Mg alloy matrix). To improve the wetting of theceramic powdery particles, which would normally not be wetted by moltenaluminum, magnesium is added to the matrix material, wherein magnesiumimproves wetting ability. Inert gas is used to prevent explosion andcorrosion/degradation during treatment of Al-Mg, e.g. handlingimpregnation, melting.

The impregnated yarn is transported through an infrared heating oven,the binder material melts and encapsulates the Al-Mg powder particles,including SiC, and holds them homogeneously distributed in between ofthe monofilaments. Lamination/calibration shapes the "green tape" into acarefully engineered preform. In order to ease the forming of thepreform a monitored infrared heat source is applied to soften thepolymer binder, and hence to improve the formability of the "green tape"during preform shaping and fix the preform during subsequent cooling. Acomplex shape with selective yarn reinforcement is preformed. Theoriginal separation between the mono-filaments and/or mono-filamentsdistribution present in the "green yarn" is maintained during shaping ofthe engineered preform.

The fibours-powdery preform is then transferred to a mould, embodyingthe shape of the final structure, and the binder is removed (by heatingunder vacuum where volatilization occurs). During this removal of thebinder material, cavities/void spaces develop in between of theentrenched Al-Mg matrix powders/SiC particulates, being hold in place inbetween of the mono-filaments. Nitrogen "cleaning gas" is applied duringbinder removal, in order to remove any contamination of the fibers orimpregnated particles.

The preform is pre-heated, and the cavities between the mono-filamentsand the particles are then vacuum infiltrated by liquid Al-Mg matrixmaterial, at 850°-950° C. under a low inert gas pressure.

In this way a shaped composite article with excellent properties andwith a substantial weight saving, e.g. 35-40%, compared to conventionalAl-Mg alloy, is obtained with sustained mechanical performance. Sincegraphite fibers have a negative thermal expansion, and aluminium apositive, the structure is engineered to have no expansion attemperature changes.

When repeating the process using other reinforcing filaments similarpreforms can be made. Instead of a metal matrix other matrix materialsor matrix combinations can be used as well.

Ceramic composites can be made in a similar way, whereby the metalparticles/molten metal form the pre-ceramic precursor material andchemical synthesis can for example be performed via an oxidationreaction between the metal and the oxidant.

Direct metal oxidation technology could also be used, whereby the(additional) metal is progressively drawn through its own oxidationproduct and the preform by capillary action to sustain the growthprocess into the preform (LANXIDE patented directed oxidation process).

Examples of ceramic matrix materials include, but are not limited to,aluminum oxide, aluminum nitride, zirconium nitride, titanium nitrideand AlN matrix.

Metallic pre-cursor fibers can be used as a fiber or part of hybridfiber material to shape the preform. They are next converted to ceramicmaterial by oxidation reaction.

EXAMPLE 2 Injection Molding of Long SiC Fiber Reinforced--AluminumArticle

Now a test is made for the high volume production of complex parts. Tapematerial similar to example 1, using a polypropylene binder, is choppedinto lengths of 10 mm. The composition of the tape is 30 vol. % SiCmonofilaments, Al-Mg alloy powder (5μm) matrix spacer particles 40 vol.% including SiC particles (0.5 μm) and binder 30 vol. %. (The Mg contentbeing 6 weight % of the Al-Mg alloy matrix).

The chopped tape is mixed with additional binder 10% and lubricant toachieve a toothpaste like mix that can be injected into a multiple mouldcavity. The injection moulded article is removed from the mould and thebinder is removed by a combination of solvent extraction and/or heattreatment, whereby the binder is broken down and vaporized. Thetreatment is continued till a minimum quantity of binder is left to keepthe shaped metal form together. The part is sintered at hightemperature. In order to minimize shrinkage, ultra fine metal particlesor molten metal can be infiltrated in the injection moulded part priorto sintering.

When repeating the process using most of the powdery metal as well asceramic materials a large variety of articles can be moulded in thisway.

EXAMPLE 3 Continuous Silicon Carbide Fiber Reinforced--SiC MatrixArticle

Continuous SiC monofilament yarn (10 μm) is homogeneously impregnatedwith a mixture of SiC powdery spacer particles (3.5 μm) and polysilanepre-ceramic polymer precursor material (particle size 10-20 μm). Inorder to tailor the interfacial bond strength, a pyrolytic carboninterface coating is applied to the SiC monofilaments.

Homogeneous impregnation is performed at high speed, using the,continuous binder/particulate powder impregnation process as describedin EP 274464, whereby binder is molten.

The composition of the tape is 50 vol. % SiC monofilaments, SiCparticles 20 vol. %, and polysilane precursor binder polymer 30 vol. %.

The impregnated yarn is transported through an infrared heating oven,the precursor binder material melts and encapsulates the SiCparticulates and holds them homogenously distributed.Lamination/calibration gives shape to the so formed "green tow".

The "green tape" is formed into a carefully engineered braided preformand combined with stacked laminates, taking care of the shrinkage onsolidification, forming the "pressure armour" and subsequently helicalpreformed tapes are wound over this structure in clockwise andanti-clockwise layers, forming the tensile armour. The preform haspre-defined .selective monofilament reinforcement according to the shapeand to the forces applied to the final cylinder structure.

The original separation between the mono-filaments and/or mono-filamentsdistribution as being present in the "green yarn" is substantiallymaintained during shaping of the engineered preform. The fibrous-powderypreform is then transferred to a mould, embodying the shape of the finalstructure, and the precursor is pyrolysed at reduced temperatures, lowenough to prevent fiber degradation. The SiC particles, homogenouslydistributed in between of the mono-filaments, hold the mono-filaments inpositive "angle plied" alignment and well spaced side by side across thepreform, which allow for a much faster and highly improved infiltrationof the second phase matrix material through chemical vapour infiltrated(CVI) by the thermal decomposition of an organo-silane,methyltrichlorosilane (MTS), in the presence of hydrogen at elevatedtemperature.

Si₃ N₄ composites can be made in a similar way, using preceramicpolysilazane binder material and chemical synthesis.

CVI, using nitrogen gas, can densify the preform after

"clean burning" binder removal or

"pre-ceramic precursor" binder synthesis.

CVI is preferably preformed at temperatures low enough (e.g. 800°-900°C.) to enhance uniform deposition/densification/infiltration and preventpremature closing of the preform-surface porosity. Other CVIpossibilities include Al₂ O₃, ZrO₂, TiB₂ and TiC. Sol-gel or Reactionbonding can also advantageously be applied. Ceramic pre-cursor fiberscan be used as a fiber or part of hybrid fiber material to shape thepreform. They are next converted to ceramic material by pyrolysation.

EXAMPLE 4 Carbon/Carbon Composite Article

Continuous graphite mono-filament yarn (diameter 10 μm) is homogeneouslyimpregnated with a mixture of graphite powdery particles 3.5 μm andpowdery polyamide (PA) binder material (particle size 10-20 μm, with anaverage of approximately 15 μm).

Homogeneous impregnation is performed at high speed, using thecontinuous binder/particulate powder impregnation process as describedin EP 274464, whereby the graphite particles are homogeneouslydistributed and the PA binder is molten. The composition of the tape is50 vol. % graphite monofilaments, graphite particles 25 vol. %, andpowdery PA binder 25 vol. %. Thus more than 75% is already composed ofcarbon materials, which dramatically reduced production time of the C/Ccomposite cone.

The impregnated yarn is transported through an infrared heating/meltingoven, the PA binder material melts and encapsulates the graphiteparticulates and holds them homogeneously distributed.Lamination/calibration gives shape to the so formed "green tape".

The "green tape" is formed into a carefully engineered preform made by acombination of braiding and edge-wise tape winding.

The preform has pre-defined selective mono-filament reinforcementaccording to the rosette shape and to the forces applied to the finalrocket exit cone structure. In order to improve the homogeneity, thepreform is baked in a hot press and then subjected to high temperatureheat treatment under inert nitrogen gas, further densified under lowheat and low pressure and formed in the shape of the final rocket exitcone structure, to enable the production of the net-shape cone.

The fibrous-powdery cone preform is then transferred to a mould,embodying the shape of the final cone structure, and the PA bindermaterial is pyrolysed by heating to over 800° C. in an inert atmosphere,leaving a carbon residue of the pyrolysed PA. The mass loss of the PAbinder, associated with the pyrolysation process is a function of thetemperature, and cavities/void spaces develop in between of the"impregnated" primary graphite particulates and PA secondary carbonmatrix material, being hold in place in between of the mono-filaments.

The cavities between the mono-filaments and the carbon particles arevacuum pressure infiltrated, with hot pitch as a source of carbon, andpyrolysed again to increase the density. After rough machining theinfiltration cycle is repeated until the required density of carbonmatrix is achieved.

The composition cone is then finished by heating to 2400° to 2800° C.,whereby the matrix undergoes a structural change into graphite.

Depending on the application, the hard carbon-carbon cone surfaces arecoated/diffusion bonded to fill the outer plies with silicon carbide andprotect the C/C composite against degradation of the properties byoxidation. Surface sealing can be applied for greater durability.

By using this process continuous fiber reinforced C/C composites, evenin complex shapes, are made more constantly and far cheaper. Because ofthe large amount of carbon already present infiltration to full densitycan be done at lower pressures and in a considerably shorter time thanwith the prior art process.

These examples involve generally similar processing schemes for preformpreparation. Improved infiltration offers the potential of substantiallygreater flexibility in processing complex net-shape composites since thepresence of homogenously distributed cavities makes the preformpermeable and thus highly facilitates the penetration of the matrixmaterial in this inter-fiber void spaces, while penetration time isdramatically shortened since a substantial part of the matrixmaterial(s) is generally present in the preform in powdery form and/orprecursor and only additional infiltration of identical or compatiblesecond phase matrix material is required.

What is claimed is:
 1. A process for manufacturing a composite productreinforced by forming a molded preform to a desired shape andsubsequently processing the preform into a final shaped compositeproduct, comprising the steps of;(a) chopping a ribbon comprising anumber of continuous longitudinally oriented fibers which are spacedfrom each other by uniformly distributed particles bonded therebetweenby a flexible precursor binder; (b) mixing the chopped ribbon with abinder and at least one of a lubricant and a matrix material to form amixture; (c) forming moldings from the mixture by a molding method; (d)converting the precursor binder into matrix material, thereby leavingvoids between the fibers and the particles; and (e) filling the voidsbetween the fibers and the particles with additional matrix material. 2.A process according to claim 1 characterized in that the uniformlydistributed particles are granules, flakes, platelets, whiskers ormixtures thereof.
 3. A process according to claim 2, characterized inthat the uniformly distributed particles comprise material which can beintegrated into the matrix material.
 4. A process according to claim 2,characterized in that the uniformly distributed particles are preencapsulated with the precursor binder so as to reduce the risk ofexplosion and oxidation of the particles.
 5. A process according toclaim 1, characterized in that the ribbon is treated such that theflexibility is improved prior to forming the preform.